Explosives

ABSTRACT

The invention relates to a new method of using explosives. 
     In the past it was the practice to use the shock wave front or the pressure pulse, or both, generated by a detonated explosive mass to directly affect a target or to deform and drive a solids element against the target. 
     In the method proposed by the present invention the explosive mass (11) and a compressible focussing means (12) are supported in a liquid medium. The focussing means (12) lie between the explosive mass and the target (T) and is spaced therefrom by liquid medium. The compressible focussing means (12) may comprise a compressible solids material or a gas volume. 
     When the explosive mass (11) is detonated the pressure pulse, and the liquid displaced by the gas bubble generated by the detonation, serve to collapse the focussing means (12), generating high pressure liquid flows directed towards the target (T).

This invention relates to a method of using explosive charges and toapparatus for practising the said method.

It is well known in the art that when an explosive charge is detonatedthe detonation produces two major effects on its immediate surroundings;

(1) shock waves, which travel outwardly in all directions from thedetonated charge, and

(2) a high pressure, generated by the gases produced by the detonatingcharge,

and in all prior methods of using explosives one or the other or both ofthe above effects are utilized directly to affect a target.

When an explosive charge is used to break rock, masonry or the likemasses the explosive is generally confined to a borehole where, ondetonation, the shock wave travels outwardly through the surroundingmass having little effect thereon whilst the high pressure developed bythe detonated charge produces such compression forces in the surroundingmass as to effect fracture along natural planes of weakness.

For convenience hereinafter the effects of the high pressure on itssurroundings shall be referred to as a "pressure pulse".

When a so called "plaster" charge is applied to one surface of a metalsheet or plate part of the shock wave travels through the metal targetto blow a so called "spall" from that surface of the metal target remotefrom the detonated charge. The spall is formed exclusively by the shockwave. The pressure pulse also effects the target and can deform themetal surface which was in contact with the detonated charge such that,if the plaster charge is sufficiently large, the target material betweenthe explosive charge and the spall cavity can be deformed, being bentinwardly to the spall cavity, and in some cases so deformed as to breakthe metal target. Thus, with this method the shock wave displaces aspall from that surface of the metal target remote from the detonatedcharge and the pressure pulse can produce deformation of the metaltarget, including a breakthrough into the spall cavity.

In a more recent use of explosives for cutting targets, such as metalsheets or plates, the explosive mass is arranged to direct two shockwave fronts simultaneously into the target to effect a break of thetarget along the line of collision of the two shock wave fronts. Thus,in this mode of operation, the target is affected essentially by theshock wave front and the pressure pulse has little effect upon thetarget.

In the well known "shaped" charge arrangement a solids element is spacedfrom a target surface and an explosive mass is detonated on that surfaceor surfaces of the solids element remote from the target. With thisarrangement the shock wave front passing through the solids element haslittle effect thereon but the pressure pulse deforms the solids elementand drives that element, in blade-like form, at very high velocityagainst the target to effect at least an indentation of the target.Thus, with this mode of operation, the useful energy of the explosivemass is directed to the deformation and acceleration of the solidselement and has little effect on the target but it is essential for allprior art methods for using shaped charges that the explosive mass beapplied directly to the solids element to ensure that the high pressurepulse has the desired effect on the solids element and the solidselement must be spaced from the target only by a vacuum, or lesspreferably a gaseous medium, as any other medium will adversely affectthe shape and velocity of the deformed solids element.

There are well known difficulties in utilizing all the aforesaid methodsof using explosives in underwater situations. Boreholes are difficult todrill accurately and the difficulties in drilling and charging boreholesincreases as the depth of the water increases. Plaster charges havelittle effect on underwater rock and masonry structures. Two shock wavecutting requires only small amounts of explosive but is relativelyineffective on rock and masonry structures. Shaped charges, requiring asthey do a complete absence of liquid medium between the solids elementand the target, are complex and expensive to produce, difficult tolocate particularly in waters of substantial depth, and as the shapedcharge is adversely affected by passage through any fluid medium suchcharges are useless when the target rock or masonry has a deposit of mudor clay or other sediment thereon and the shaped charge constructioncannot be located directly in contact with the solid target to beaffected.

The present invention seeks to provide a new method and apparatus forusing explosive charges and which method and apparatus has particularadvantages in underwater applications.

According to the present invention there is provided a method of usingexplosives characterised by the steps of locating an explosive mass in aliquid medium in spaced relationship to a target, locating acompressible focussing means between the said explosive mass and thesaid target, the focussing means being spaced from said explosive massby liquid medium, and detonating said explosive mass to drive liquidmedium through said focussing means to the said target.

It will now be seen that the method of using explosives proposed by thepresent invention is quite different and distinct from all the prior artmethods described hereinbefore in that the proposed method does not relyon the shock wave or the pressure wave generated by the detonatedexplosive mass to affect the target.

In practice of the method proposed by the present invention thedetonation of the explosive mass generates a pressure front whichexpands outwardly through the liquid medium until part of said pressurefront contacts the compressible focussing means, the pressure wavecauses the focussing means to collapse in the direction of the targetand the rapid collapse of the focussing means generates a very highvelocity flow in the liquid directed towards the target.

It will be noted that the method proposed by the invention does notessentially require the target to be surrounded by the liquid medium asit has been found in practice that high speed velocity flows can begenerated to affect a target outside the liquid medium.

In one embodiment in accordance with the invention the said focussingmeans comprise a body of compressible solids material.

In another embodiment in accordance with the invention the saidfocussing means comprise a gaseous volume. Preferably the said gaseousvolume is contained in a preformed collapsible envelope.

In another embodiment in accordance with the invention the said gaseousvolume is defined by releasing gas bubbles from a gas source.

In a further embodiment in accordance with the invention the saidgaseous volume is generated by detonating an explosive material.

In one embodiment in accordance with the invention the method ischaracterised by the steps of arranging a plurality of focussing meansbetween the explosive mass and the target, said focussing means being inspaced relationship with liquid medium therebetween, and arranged tosuccessively focus energy generated by the detonated explosive masstowards the target.

In another embodiment in accordance with the invention the method ischaracterised by the steps of arranging a plurality of focussing meansbetween the explosive mass and the target such that each focussing meansserves to focus energy generated by the detonated explosive mass to thetarget along a direction individual to that focussing means.

The present invention also envisages apparatus for carrying out themethod comprising an explosive mass, one or a plurality of compressiblefocussing means, and means for supporting said explosive mass and saidfocussing means in fixed, spaced apart relationship.

In another embodiment the apparatus includes an explosive mass and meansfor producing one or a plurality of gas volumes between said explosivemass and a target.

The invention will now be described further by way of example withreference to the accompanying drawings in which;

FIG. 1 shows, diagrammatically, one embodiment in accordance with theinvention.

FIGS. 1a, 1b, 1c and 1d show, diagrammatically, the effects of theembodiment shown in FIG. 1 at different stages following detonation.

FIG. 2 shows, diagramatically, a second embodiment of the inventionutilizing a shaped explosive charge.

FIG. 3 shows, diagramatically, a third embodiment of the inventionutilizing a compressible solids focussing means,

FIG. 4 shows, diagramatically, a further embodiment in accordance withthe invention utilizing a plurality of focussing means and.

FIG. 5 shows, diagramatically, a further embodiment of the inventionutilizing a plurality of focussing means between the explosive mass andthe target.

In the illustrated examples identical elements are identified by thesame numerals.

In the embodiment illustrated in FIG. 1 an explosive mass 11 and anexplosive charge 12 are supported in spaced apart relationship by twolimbs 13a and 13b respectively of an inverted U shaped frame element 13.Two cables 14 and 15, secured to the bridge 13b of element 13 at spacedapart locations, support the apparatus from a flotation member (notshown) on the surface of the water. Thus, the depth of the element 13can be adjusted by adjusting the lengths of the cables 14 and 15. Withthe cables 14 and 15 secured to spaced apart locations on the flotationmember the apparatus as illustrated can be rotated about a vertical axisby simply rotating the flotation member. Thus, by this means, theelement 13 can be located in any desired position relative to a targetT, the explosive charge 12 is detonated and the high pressure, hightemperature gases generated by the detonation produce a bubble 12a.

As is well known in the art the detonation of an explosive chargeproduces very high temperature and high pressure gases, the pressure ina bubble generated by a detonated explosive can initially exceedthousands of tons per square inch and the high pressure in the gasbubble is transmitted to the surrounding liquid medium to causes thesurrounding media, to be displaced violently in all directions away fromthe centre of the gas bubble to allow the bubble to expand.

With the violent displacement of the surrounding media away from thedetonated charge the gas bubble expands, the pressure in the bubblefalls, and at that point where the momentum in the surrounding media isarrested the pressure in the bubble can be less than the surroundingpressure of the liquid. At this point of maximum volume of the bubblethe system implodes and the surrounding media flows inwardly to collapsethe bubble. Being a compressible mass the bubble will reduce in volumeto a point at which its internal pressure exceeds the pressure of thesurrounding media, when again the bubble will expand. Such a bubble,produced by detonation of an explosive charge, will experience a seriesof expansion/contraction cycles before it reaches a state ofequilibrium. Such behaviour of a bubble, generated by detonation of anexplosive charge, is well known in the art.

In accordance with the present invention the explosive mass 11 isdetonated after the explosive charge 12 and, in like manner to thedetonation of charge 12, the detonation of explosive mass 11 generates ahigh pressure, high temperature gas bubble which expands displacing thesurrounding water violently away from the centre of the gas mass.

The delay period between the detonation of the explosive charge 12 andthe explosive mass is 11 preferably so selected that the gas bubble 12ais substantially at its maximum volume, lowest pressure condition atthat point when the pressure pulse generated by the expansion of thebubble 11a, reaches the bubble 12a. At this point the displacement ofwater by the bubble 12a towards the bubble 11a is minimal but the bubble11a is generating pressure pulse in the water and the water between 11aand 12a, is at high pressure and is being driven towards bubble 12a,whereupon that part of bubble 12a towards bubble 11a is collapsed,generally as shown in FIG. 1b. With the collapse of that side of thebubble 12a towards bubble 11a the high pressure water is focused by theinterface between the gas bubble 12a and the surrounding media andproduces a high velocity flow which passes through the bubble 12a thusforming the bubble 12a into an annulus, and the high velocity flowstrikes the target T. Whilst the pressure pulse is being continued bythe bubble 11a the high pressure jet through bubble 12a will bemaintained but the high velocity flow of the water in the direction fromthe bubble 11a to bubble 12a will entrain surrounding water and, withthe release of pressure in the surrounding media between bubble 11a andbubble 12a, the bubble 11a will be drawn towards the bubble 12awhereupon, as it approaches bubble 12a the effect of the expansions ofbubble 11a, due to its cyclic pulses, will assist the maintenance ofhigh pressure flows through the bubble 12a to the target T.

The formation of the bubble 12a into annular form, with displacement ofthe bubble 11a towards the annulus 12a is shown in FIG. 1c and thecontinuing expansion of the bubble 11a, with degradation of the annulus12a is shown in FIG. 11d.

It will be seen from the above that the system according to the presentinvention, produces high velocity liquid flows against the target andwhich high velocity flows can have a greater effect upon a rock ormasonry target than any prior art underwater explosive arrangement knownto date.

Further, with the formation of the gas bubble 12a generating pressurepulses through the water, with pressure flow of the water, deposits onthe target T can be displaced thereby but, in the event, the highvelocity liquid flows will cut through any sedimentary deposit to affectthe target T.

In the arrangement shown in FIG. 2 the explosive charge 12, supported bythe limb 13b of element 13, is of elongate form with its longitudinalaxis extending between the explosive mass 11 and the target T. Asillustrated, the explosive charge 12 reduces in cross section from itslargest cross section nearest the explosive mass 11, towards the target.Such an arrangement, on detonation of the explosive charge 12, producesan elongate gas bubble which is most effective in focussing the liquidflows towards the target.

In the arrangement illustrated in FIG. 3 the limb 13b of element 13supports a truncated conical body 16 the axis of which extends in thatdirection between the explosive mass 11 and the target T.

The body 16 may comprise a gas-filled envelope or a body of solidsmaterial, such as an expanded polystyrene, and the essential feature ofthe body 16 is that it must be compressible when struck by the pressurepulse generated by detonation of the explosive mass 11. Thus, ondetonation of the explosive mass 11, the pressure pulse in thesurrounding water generated by the expansion of the gas bubble 11acauses that end of body 16 nearest the bubble 11a to collapse inwardlyof the body 16, the water flows into and through the collapsible body 16being focused by the disrupted or deformed body 16 to generate highvelocity water flows towards the target T.

In the embodiment illustrated in FIG. 4 a frame, generally indicated bynumeral 17, comprises a horizontal or bridge element 17a, supported bycables 14 and 15 in identical manner to the prior embodiments, withthree limbs 17b, 17c and 17d depending downwardly therefrom. The outerlimbs 17b and 17d support bodies 18 and 19 and the central 17c supportsan explosive mass 11 and a focussing body 20.

The focussing bodies 18, 19 and 20 are identical in their shape andconfigurations and may be substantially identical to the body 16illustrated in FIG. 3 and may, therefore, conveniently comprise gasfilled envelopes or compressible bodies of solids material or anycombination of both. Each of the bodies 18, 19 and 20 is of generallytruncated conical form, the central axis of the body 18 liessubstantially horizontal with the greatest cross section of the crosssection form nearest the explosive mass 11, the body 19 has its axissubstantially horizontal with the major cross section of its formadjacent the explosive mass 11, and the body 20 has its axis verticalwith its major cross section nearest the explosive mass 11. The bodies18, 19 and 20 are equally distant from the explosive mass 11.

In the example illustrated in FIG. 4 the arrangement is located in atrough or channel filled with water and that side of the channeladjacent body 18 comprises target T1, that side of the channel adjacentbody 19 comprises target T2, and the base of the channel, adjacent body20, comprises target T3.

With the arrangement correctly located in the channel the explosive mass11 is detonated and the pressure pulse in the water generated by theexpansion of the gas bubble 11a is transmitted simultaneously to thethree bodies 18 19 and 20, that end region of each body 18 19 and 20nearest the gas bubble 11a will collapse under the pressure wave andhigh velocity water flows will be generated and focussed through thecompressible bodies 18, 19 and 20. The compressible body 18 will focusthe high velocity water flows therethrough against the target T1, thebody 19 will focus the high velocity flows therethrough against thetarget T2 and the body 20 will focus high velocity flows against the thebase of the channel, target T3. Thus, high velocity water flows can befocused in different directions from a single explosive mass 11.

In the example illustrated in FIG. 5 a weighted, gas bubble releaseblock 21 rests on the bottom and is connected to a locating vessel onthe surface by a cable 22. The cable 22 may conveniently comprise a gashose through which gas can be pumped from the surface vessel to the gasrelease block 21. With this arrangement the surface vessel can tow theblock 21 over the surface of the bottom below the water as and until theblock 21 is located in the desired position. Thereafter, the explosivemass 11 is lowered to a desired position directly above the block 21 andis detonated whilst the block 21 is releasing bubbles.

When the explosive mass is detonated the pressure pulse acts on all thebubbles between the expanding bubble 11a and the block 21, each bubblewill focus the water driven against its collapsed upper end (that endclosest to the gas bubble 11a,) and the overall effect is a plurality offocusing devices between the gas bubble 11a and the bottom which resultsin an overall high velocity flow of water against the bottom.

It will be appreciated that the effects of the high velocity follows,generated by collapse of compressible body or bodies, will be dependantupon the distance between the focusing device and the target but inpractice high velocity flows can be experienced more than a meter beyondthe focusing means.

It will be appreciated that the method proposed by the present inventioncan be practised to obtain a high pressure liquid flow concentrated onrelatively small areas of the target or on a relatively large area ofthe target, dependant upon the result desired, but the method can bepractised in many ways and, by way of example, two explosive charges ofelongate form of any desired length, with means for supporting the saidcharges in spaced apart relationship, can be detonated as proposed bythe present invention to direct a knife-like high velocity water flow,of a length substantially equal to the length of the combined explosivecharges, against a target.

Further, the target need not essentially be within the liquid medium andthe method proposed by the present invention can be practised togenerate high speed velocity flows capable of passing upwardly throughthe free surface of the liquid medium to affect a target outside theliquid medium.

I claim:
 1. A method of using explosives characterised by the stepsof:(a) locating an explosive mass in a liquid medium in spacedrelationship to a target, (b) locating a compressible focussing meansspaced from said explosive mass by liquid medium between said explosivemass and said target, and (c) driving liquid medium through saidfocussing means to the said target by detonating said explosive mass. 2.A method according to claim 1 characterised in that the said focussingmeans comprise a body of compressible solids material.
 3. A methodaccording to claim 1 characterised in that the said focussing meanscomprise a gaseous volume.
 4. A method according to claim 3characterised in that the said gaseous volume is contained in apreformed collapsible envelope.
 5. A method according to claim 3characterised in that said gaseous volume is defined by releasing gasbubbles from a gas source.
 6. A method according to claim 3characterised in that said gaseous volume is generated by detonating anexplosive material.
 7. A method according to claim 1 characterised bythe steps of arranging a plurality of focussing means between theexplosive mass and the target, said focussing means being in spacedapart relationship with liquid medium therebetween and arranged tosuccessively focus energy generated by the detonated explosive masstowards the target.
 8. A method according to claim 1 inclusivecharacterised by the steps of arranging a plurality of focussing meansbetween the explosive mass and the target such that each focussing meansserves to focus energy generated by the detonated explosive mass to thetarget along a direction individual to that focussing means. 9.Apparatus which comprises an explosive mass, one or a plurality ofcompressible focussing means, and means for supporting said explosivemass and said focussing means in fixed, spaced apart relationship. 10.Apparatus which includes an explosive mass and means for producing oneor a plurality of gas volumes between said explosive mass and a target.11. A method according to claim 2 characterized by the steps ofarranging a plurality of focussing means between the explosive mass andthe target, said focussing means being in spaced apart relationship withliquid medium therebetween and arranged to successively focus energygenerated by the detonated explosive mass towards the target.
 12. Amethod according to claim 3 characterized by the steps of arranging aplurality of focussing means between the explosive mass and the target,said focussing being in spaced apart relationship with liquid mediumtherebetween and arranged to successively focus energy generated by thedetonated explosive mass towards the target.
 13. A method according toclaim 2 characterized by the steps of arranging a plurality of focussingmeans between the explosive mass and the target such that each focussingmeans serves to focus energy generated by the detonated explosive meansto the target along a direction individual to that focussing means. 14.A method according to claim 3 characterized by the steps of arranging aplurality of focussing means between the explosive mass and the targetsuch that each focussing means serves to focus energy generated by thedetonated explosive mass to the target along a direction individual tothat focussing means.